Understanding C++ Program Structures: Functions, Scope, and Compilation Process

1. Chapter 4 functions and program structure Speaker: Lung-Sheng Chien

2. OutLine • Example: grep - organization of program structure- compilation process • Precedence and Associativity • External/Internal objects • Scope and Lifetime • Preprocessor (前處理器)

3. grep – print lines matching a pattern Ah Love! could you and I with Fate conspire To grasp this sorry Scheme of Things entire, Would not we shatter it to bite -- and then Re-mould it nearer to the Heart’s Desire! Search for the pattern “ould” Ah Love! could you and I with Fate conspire Would not we shatter it to bite -- and then Re-mould it nearer to the Heart’s Desire!

4. Structure of the program Function getline Pseudocode while ( there is another line) if ( the line contains the pattern ) then print it endif endwhile Function strindex Function printf File getline.cpp File strindex.cpp File main.cpp function strindex function getline function main (driver) call

5. grep project – getline function [1] Project  Add to Project  New 1. project grep 2. source file getline.cpp

6. grep project – getline function [2] 1. Source file getline.cpp Q1 Q2 definition of getline Question 1: why we need input parameter lim? Question 2: what is execution order in predicate of while-loop?

7. grep project – strindex function [1] Project  Add to Project  New 1. project grep 2. source file strindex.cpp

8. grep project – strindex function [2] source file strindex.cpp definition of strindex Question: what is procedure of function strindex ?

9. grep project – main function [1] Project  Add to Project  New 1. project grep 2. source file main.cpp

10. grep project – main function [2] declaration, not definition source file main.cpp remember to add new line character Question: who does function main return found to ?

11. grep project – in Linux machine Upload project grep by sftp first 1. compile 3 source files 2. feed article.txt into a.out article.txt Ah Love! could you and I with Fate conspire To grasp this sorry Scheme of Things entire, Would not we shatter it to bite -- and then Re-mould it nearer to the Heart’s Desire! 3. 上一個指令的傳回值

12. “grep” is embedded in Linux machine Search manual of grep 1. pattern 2. File

13. Function definition 白話文 return-type function-name ( argument declarations) { declarations and statements } 文言文 (grammar, page 234, 235) function-definition: declaraction-specifiers(opt)declarator declaraction-list(opt) compound-statement declarator: pointer(opt) direct-declarator declaration-specifier: storage-class-specifier declaration-specifier(opt) type-specifier declaration-specifier(opt) type-qualifier declaration-specifier(opt) direct-declarator: Identifier direct-declarator( parameter-type-list )

14. definition of main function [1] declaraction-specifiers declarator compound-statement type-specifiers

15. definition of main function [2] declarator: Pointer(opt) direct-declarator direct-declarator: direct-declarator ( parameter-type-list ) Identifier compound-statement: { declaration-list statement-list }

16. Why we need declaration of getline and strindex in main.cpp Compiler 是逐個檔案作編譯, 當他讀main.cpp 且看見 getline(line, MAXLINE) 時需作 type checking, 可是 getline 的 defintion 是在 getline.cpp 內, 並不在 main.cpp, 所以我們需在 call getline 之前宣告 getline 的原型, 注意: compiler 只讀檔一次, 所以必需在compiler作 type checking 之前就告訴他函數的原型

17. 編譯順序 -- [1] main.cpp 秀出編譯過程 c++ 編譯器 編譯為組合語言 先編譯 main.cpp 翻譯組語成 object code, ccEg6xsf.o檔 GNU assembler

18. 編譯順序 -- [2] getline.cpp c++ 編譯器 編譯為組合語言 再編譯 getline.cpp 翻譯組語成 object code, ccnNjsxn.o檔

19. 編譯順序 -- [3] strindex.cpp c++ 編譯器 編譯為組合語言 最後編譯 strindex.cpp 翻譯組語成 object code, ccQJUtuu.o檔

20. 連接程序 – linking process Collect2 被作為ld (GNU linker 連接器 ) strindex.cpp main.cpp getline.cpp Source code Compiler g++ / icpc Assembler as Linker collect2 / ld Executable file a.out Assembly code .s file object code .o file

21. OutLine • Example: grep • Precedence and Associativity • External/Internal objects • Scope and Lifetime • Preprocessor (前處理器)

22. Precedence and Associativity of operators [1] Execution order Q2 Question 2: what is execution order in predicate of while-loop?

23. Precedence and Associativity of operators, page 53 [2] arithmetic, 先乘除後加減 relational logical assignment Precedence : () > arithmetic > relational > logical > assignment

24. Parsing tree of • Execution order • bottom-up • Left subtree  right subtree associativity of && is left to right != is higher than && > is higher than && != is higher than && -- is higher than > () is higher than !=

25. Three equivalent coding style 用括號表示優先次序 c is well-defined

26. Question: what’s procedure of function strindex ?

27. OutLine • Example: grep • Precedence and Associativity • External/Internal objects • Scope and Lifetime • Preprocessor (前處理器)

28. External/internal objects [1] • External objects- external variable (global variable): defined outside any function- functions • Internal objects- variables inside function without declaring static- parameters of a function Grammar in page 234 translation-unit: external-declaration translation-unit external-declaration external-declaration: function-definition declaration declaration: declaration-sepcifiers init-declarator-list(opt)

29. External/internal objects [2] file main.cpp External variable’s definition Local variables External object: function main

30. Local variables External object: function strindex file getline.cpp file strindex.cpp Local variables External object: function getline

31. OutLine • Example: grep • Precedence and Associativity • External/Internal objects • Scope and Lifetime • Preprocessor (前處理器)

32. Scope and visibility • The scope of a name is the part of the program within which the name can be used. • For automatic variable (automatic storage) declared at the beginning of a function, the scope is the function in which the name is declared. • Local variables of the same name in different functions are unrelated. The same is true of the parameters of the function, which are local variables also. • The scope of an external variable or a function lasts from the point at which it is declared to the end of the file being compiled. • External variable in file1 can be accessed by functions in file2 if it is declared by keyword extern in file2. • staticexternal variable is encapsulated inside a file1, no other functions of file2 can access it.

33. Scope graph Level 0 Level 1 Level 2 block scope

34. Lifetime (生命周期) [1] • “Lifetime” is the period during execution of a program in which a variable or function exists. The storage duration of the identifier determines its lifetime. • Identifiers with static storage duration (global lifetime) are alive during (main) program execution and die when program terminates.Example: global variable, static variable • Identifiers, which are defined inside a function, with automatic storage duration(local lifetime) is allocated new storage each time the function is called and die when function returns.Example: local variable, function parameter • Although an identifier with a global lifetime exists throughout the execution of the program, it may not be visible in all parts of the program.

35. Lifetime (生命周期) [2]

36. MSDN Library: search “extern” extern and static [1] • A variable declared with the externstorage-class specifier is a reference to a variable with the same name defined at the external level in any of the source files ofthe program. • The internal extern declaration is used to make the external-level variable definition visible within the block. • Unless otherwise declared at the external level, a variable declared with the extern keyword is visible only in the block in which it is declared. global variable

37. extern and static [2] file main.cpp definition file strindex.cpp declaration

38. OutLine • Example: grep • Precedence and Associativity • External/Internal objects • Scope and Lifetime • Preprocessor (前處理器)

39. CProProcessor (cpp) [1] • File inclusion#include “filename”#include <filename> • Macro (巨集) substitution#define forever for ( ; ; ) // infinite loop#define square(x) (x)*(x) • Conditional inclusion#ifndef _INC_STDIO#define _INC_STDIO /* content of stdio.h */#endif /* _INC_STDIO */

40. CPreProcessor (cpp) [2] Source code C preprocessor cpp Compiler g++ / icpc Assembler as Linker collect2 / ld Executable file a.out Assembly code .s file object code .o file

41. CPP – macro substitution Question: Why no max operation in math.h cpp handles this but the compiler don’t see this statement

42. CPP - #include “filename” [1] cpp 會複製 stdio.h 到此檔案以便 compiler 作 type checking cpp 將替換 HELLO_STRING 輸出至檔案main_cpp.txt 讀檔案 main_cpp.txt一次一頁

43. CPP - #include “filename” [2] line 28, include feature.h 按空白鍵接下一頁 Recursively file inclusion, 需滿足因果律

44. CPP - #include “filename” [3] standard input standard output

45. CPP – conditional inclusion [1] 如果巨集 _WIN32 或巨集 __WIN32__ 有定義, 則執行程式碼 printf("This is Win32 Application\n"); 否則執行程式碼 printf("This is Linux Application\n"); Result in Visual Studio Result in Linux

46. CPP – conditional inclusion [2] Macro _WIN32 is always defined in Visual Studio

47. CPP – causality (因果律) [1] add header file getline.h content of getline.h

48. CPP – causality (因果律) [2] add header file strindex.h content of strindex.h

49. CPP – causality (因果律) [3] Question 1: why we have infinite recursion? Question 2: How to solve infinite recursion?

50. CPP – causality (因果律) [4] getline.h strindex.h getline.cpp strindex.cpp